A refrigerator is an apparatus for keeping foods stored therein in a cool and fresh state using cold air generated by a refrigerating cycle in which processes of compression-condensation-expansion-evaporation are continuously executed.
A refrigerating cycle within a refrigerating chamber includes a compressor compressing refrigerant, a condenser condensing high-temperature and high-pressure refrigerant compressed in the compressor in a manner of radiating heat, and an evaporator cooling surrounding air by a cooling operation that refrigerant introduced from the condenser absorbs latent heat while evaporated. A capillary or an expansion valve is provided between the condenser and the evaporator to increase a flow rate of the refrigerant and reduce pressure, to facilitate the evaporation of the refrigerant introduced into the evaporator.
A cooling method of the refrigerator may be divided into an indirect cooling method and a direct cooling method.
The indirect cooling method is a method of cooling an inside of a storage chamber by forcibly circulating cold air generated in the evaporator using a blowing fan. In general, the indirect cooling method is applied to a structure in which a cooling chamber with the evaporator installed therein is separated from a storage chamber storing foods.
The direct cooling method is a method of cooling an inside of the storage chamber by natural convection of the cold air generated in the evaporator. The direct cooling method is generally applied to a structure in which an evaporator is formed in a shape of an empty box so as to form the storage chamber storing food therein.
In general, the direct cooling type refrigerator employs a roll-bond type evaporator having a cooling passage, which is formed between pressure-welded two case sheets to allow the flow of refrigerant therealong in a manner of pressure-welding the two case sheets with a pattern part interposed therebetween, sending high-pressure air to the press-welded pattern part to discharge the pattern part, and expanding a portion where the pattern part has been present.
Meanwhile, due to a difference of relative humidity between a surface of the evaporator and surrounding air, moisture is condensed on the surface of the evaporator and sometimes implanted as frost. The frost implanted on the surface of the evaporator brings about lowered heat-exchange efficiency of the evaporator.
For the indirect cooling type refrigerator, a defrosting heater is installed at the evaporator for removing the frost implanted on the evaporator. The defrosting heater is driven (turned on/off) according to a preset condition to generate heat, thereby melting the frost implanted on the evaporator.
In relation to the indirect cooling type refrigerator, a structure in which a refrigerant tube and a defrosting heater are disposed at a lower portion of a heat-exchange plate inclined by a predetermined angle (refer to the following prior art document).
However, the prior art has a fundamental problem of a low cooling effect due to increased contact resistance between the refrigerant tube and the heat-exchange plate resulting from that the refrigerant tube is attached on the heat-exchange plate.
Also, the evaporator in the form of the heat-exchange plate has difficulty in ensuring a capacity of a freezing chamber of a small refrigerator, which is difficult to be designed into multiple steps. In relation to this, when the heat-exchange plate is designed into one step, cold air flows downward due to a convection current, and thus foods on the heat-exchange plate are rarely maintained in a low-temperature state, compared with foods below the heat-exchange plate, due to a lowered cooling effect. In addition, when the heat-exchange plate is installed in a multi-step form, a welded portion of the refrigerant tube increases, which is not proper for a mass production of the evaporator.
These problems can be solved by the roll-bond type evaporator. However, a structure employing a defrosting heater at the roll-bond type evaporator has not been introduced yet.
Therefore, for a direct cooling type refrigerator with the roll-bond type evaporator, in order to remove frost, a compressor is forcibly turned off and thereafter natural defrosting should inconveniently be executed for a predetermined time. The long defrosting time causes difficulty in ensuring freshness of foods.